Hi KateC4
any lot can only have 20 Sims on a vanilla game. Unfortunately when you remove mods, Sims that are over the max are not removed from the game unless you go to CAS.
If you overstuff your households but don't have the mod in to allow more than 20 Sims, any lot will already be full and not spawn new Sims. Each household member counts for 1 Sim whether they are on the lot or not.
Try putting back the mod that helps you with overstuffing (make sure it's updated) and see if it then works.
Moving this to the mods forum for further help.